ASoC: rsnd: remove struct rcar_snd_info

No board is using Renesas sound driver via platform boot now.
This means all user is using DT boot. Platform boot support is
no longer needed. But, it strongly depends on platform boot style.
Now, platform boot style was removed from driver.
This is cleanup patch, and remove pointless struct rcar_snd_info

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>